One of the paramount goals of orthodontic treatment has been to have the mesial and distal contacts of the teeth of the patient in an arch that is parallel to the dental archform. In order to achieve this with a smoothly bent archwire, orthodontic appliances have been constructed using an archwire that is shaped to an archform that is mathematically similar, or parallel, to the dental archform of the patient. However, because the different teeth of the patient are of differing thicknesses, this goal has required the use of larger brackets on the smaller teeth of the patient and, conversely, smaller brackets on the thicker teeth of the patient, so as to provide a constant spacing between the archwire and dental archform.
Providing higher profile brackets on the smaller teeth is particularly troublesome on the lower anterior teeth, which are the smallest teeth of the patient. As a result of the use of the thickest brackets on these lower anterior teeth, the appliance presents a higher profile, that is, extends farther from the tooth in the labial-lingual direction. In such higher profile appliances, the archwire is supported in a position spaced away from the face of the tooth, compromising the performance of the appliance in many ways.
For example, increased spacing of the archwire from the tooth unfavorably increases the moments about the center of resistance of the tooth. In addition, the higher profile brackets often result in the need to compromise the placement of the brackets on rotated or otherwise misaligned teeth. Furthermore, the higher profile brackets place greater loads on the bracket-to-tooth adhesive, contributing to an increase in the likelihood of failure of the bond.
Additionally, the larger brackets interfere with oral hygiene, increasing enamel decalcification and compromising gingival health.
Therefore, it is desirable to provide orthodontic appliances with brackets that provide as low a profile as possible. In the prior art, however, the need to provide a minimum archwire spacing from the thicker teeth has prevented the use of lower profile brackets on the thinner teeth, while preserving other previously accepted requirements of orthodontic appliance design.
In providing appliances having archwires that are parallel to the dental archform, the brackets employed have had slots to receive the archwires, with slot bottoms that are parallel the archform. Such slot bottoms have been generally parallel to the bracket bases so that, when the brackets are mounted on the teeth of the patient, they support the archwire and maintain the archwire and the dental archform of the teeth in a parallel relationship. One exception to the traditional bracket configuration has been in what is known as the Roth line of treatment which calls for overcorrection of the teeth by imparting a rotation of the teeth relative to the archwire. This has entailed configuring certain of the brackets so that the slots are rotated, relative to the bracket bases and the mounting surfaces of the teeth, in a positive direction, that is in a direction that spaces the mesial end of the slot farther from the tooth than the distal end. This rotation nonetheless maintains the slot bottoms and archwire parallel to the archform of the teeth. This technique of positively sloping the bracket slots for overcorrection has been employed in brackets for the cuspids and the teeth distal thereto.
The orthodontic practices of the prior art have, nonetheless, produced appliances which, when installed on the teeth of patients, have profiles that are not optimally low, and, if modified by the replacement of smaller brackets to produce a lower profile, do not function effectively to position the teeth on a suitable archform. Unwanted tooth rotation during treatment, such as to the lower cuspid result in the prior art configurations, requiring first order bends in the archwire, for example, mesial to the cuspid bracket to prevent the cuspid rotation. For these and other reasons, it is apparent that there is a need for an orthodontic appliance having a low profile and simultaneously achieving the other orthodontic appliance design objectives.